It is well recognized that thermal energy storage, through the use of phase change materials, is of value in passive solar applications for the heating of buildings. These phase change materials absorb heat via changing from a solid to a liquid, during the presence of solar heat impinging upon the material. Then, during the time when there is no heat input to the building from the sun, the materials release heat into the building as the phase change material returns to a solid state. The particular phase change material, referred to hereinafter as a PCM, is chosen for its melting and solidification temperatures to match the particular application.
In some applications, the PCM is placed within containers positioned within the area that is to be heated. Still other installations utilize the PCM within containers positioned within the walls of the area. The earliest of PCM's were water/ice and various organics and salts exhibiting melting/thawing characteristics over a few degrees of temperature change.
In relatively recent developments, the PCM is made a part of the structural building materials, and particularly in gypsum wallboard. Apparently paraffin and paraffin-like materials, even in their melted states, adhere to the large surface area provided by the dendritic needles of calcium sulfate comprising the core of the wallboard. In particular, up to 30 wt % paraffin has been incorporated into gypsum wallboard during investigations at the University of Dayton Research Institute, Dayton, Ohio. The University of Dayton research is detailed in U.S. Pat. Nos. 4,908,166 and 5,053,446 issued to I. O. Salyer on Mar. 13, 1990 and Oct. 1, 1991, respectively. Further, initial studies have demonstrated that this composition has about the same flammability as ordinary wood such that no additional danger is created within a generally wooden structure. While the incorporation of a PCM (such as paraffin) will be of assistance in passive solar heated buildings, relatively few buildings are utilizing passive solar heating systems and therefore the wall board incorporating the PCM has little commercial use for this application.
In contrast, there exists a large use of electrical power for heating and cooling of buildings. Due to the demand upon electric utilities, load management practices have been encouraged among users. One type of electric load management has been the use of timers such that some heating requirements (as the heating of water) occurs during off-peak periods. However, load management by power interruption in systems for heating and cooling is difficult, particularly for residential use.
Other references relevant to the use of phase change materials are U.S. Pat. Nos. 4,294,078 issued to C. D. MacCracken on Oct. 13, 1981; 4,332,690 issued to H. Kimura et al, on Jun. 1, 1982; 4,360,442 issued to J. D. Reedy et al, on Nov. 23, 1982; 4,498,459 issued to E. Korin et al on Feb. 12, 1985; 4,532,917 issued to D. C. Taff et al, on Aug. 6, 1985; and 4,924,935 issued to W. V. Winckel on May 15, 1990.
Accordingly, it is an object of the present invention to provide a system for electrical load management for buildings that continues to serve the building's thermal demand while discontinuing power consumption during periods of high demand upon an electric utility.
It is another object of the present invention to utilize phase change materials to distribute a selected temperature within a building over extended time periods.
A further object of the present invention is to utilize phase change materials incorporated into building construction materials such that temperatures within a building are modified with an accompanying management of the electrical load supplied to the building.
Another object of the present invention is to utilize gypsum wallboard having incorporated therein a phase change material, with such wallboard in different portions of the structure having different phase change materials so as to optimize electrical load management of buildings during both heating and cooling cycles.
These and other objects of the present invention will become apparent upon a consideration of the drawings that follow together with a complete description thereof.